Wine grape challenges of the 2010 season

Overall conditions were conducive to powdery mildew, but there were enough washing rains and very cool temperatures, so that problems were scattered and light where normal control programs were followed.
The big concerns on the mind of many growers were new pests.
The overall crop came in well below last year’s crop and slightly less than average in yield for most varieties in most sites.

Paul Verdegaal, Viticulture Advisor, Field Notes, UCCE | Nov 17, 2010

The 2010 season presented interesting challenges to growers both long-experienced and relatively new. With the World Series under way, what comes to mind is after several very warm years Mother Nature decided on a changeup. Budbreak began slightly behind average, with weather conditions somewhat rainy and very mild the entire season. One grower mentioned they would rather grow grapes in a hot year as opposed to a cool year, as challenges seem more straightforward. That being said, fruit quality appears to be excellent, with good colors, nice flavors and higher total acids and lower pH. The double-edged sword is a light crop; the early spring rains and continued cool temperatures did reduce cluster development, flower set, and yield. Individual growers sacrifice income, but that should avoid an oversupply of wine as the economy struggles.

Overall conditions were conducive to powdery mildew, but there were enough washing rains and very cool temperatures, so that problems were scattered and light where normal control programs were followed. The early May rain of more than an inch helped reduce stress on vines and might have been part of the reason mite problems appeared light, as with leafhoppers. Compared to last year, this season there was less summer (sour) bunch rot in tight-clustered and thin-skinned varieties such as Zinfandel and Petite Sirah.

The big concerns on the mind of many growers were new pests to the county; light brown apple moth (LBAM) found in the south county in 2009, spotted wing Drosophila (SWD) also found in 2009, and European grapevine moth (EGVM) found in August of this year in east Lodi. The good news seems that SWD doesn‘t damage wine grapes as much as cherries or bush berries. The bad news has been that both EGVM and LBAM require quarantines and compliance agreement programs for growers in affected areas, as well as the added cost of possible treatments. Fortunately, only two EGVM were found and no new finds have occurred.

Overall crop

The overall crop came in well below last year’s crop and slightly less than average in yield for most varieties in most sites. The cool temperatures delayed harvest to the later side of the long-term average for early varieties such as Pinot grigio, Chardonnay, Sauvignon blanc, and Pinot noir going to sparkling wine production. White Zinfandel harvest began in earnest around Aug. 18, compared to a long-term average of about Aug. 10, and at about the same time as last year, possibly due to the lighter crop this year.

Many of the mid-season varieties sped up in development with a hot spell as harvest began and varieties such as Sangiovese, Syrah, and red Zinfandel were ready about the same time as last year. It seems the traditional core of the Lodi District caught up in fruit development; while the margins of the District to the east and west remained delayed as was most of the coast and foothills. A trace of rain occurred on Oct. 5, but a late-season warm spell before and after allowed rapid fruit ripening ahead of the initial rain of Oct. 17 with about 0.25 inch.

As harvest continued, fall weather turned for the worse; when more than 1.5 inches to 2 inches of rain fell with 30 mph winds, over two days on Oct. 23-24. Although not as bad as last year‘s deluge of 2.9 inches and 40 mph plus winds on Oct. 13, a small percentage of fields were still waiting to be picked. The ground was dry enough from the three-year drought that the rain soaked in fast. Most remaining blocks should have been harvested before significant negative effects of breakdown developed. But it‘s never good.

The 2010 season received above-average rainfall. The last rain occurred on May 27 for a seasonal total of 19.2 inches; compared to 15.1 inches in 2009, 13.6 in 2008 and 12.1 in 2007. However, vineyards need another wet winter to totally recover from the dry conditions. From mid-July on, most daily maximums were below average, but even when daytime maximums were average or higher, the nighttime lows consistently were at or just slightly above record lows each morning with very little dew. Accumulated stress, unusually cool spring growing conditions, and unexplained problems were very evident in farm calls this year. Even with above-average irrigation programs, there was only moderate growth in many vineyards, especially younger vines. And there were many vineyards with late-season berry shrivel or parts of clusters raisining. Often these problems were not attributable to disease, nutrient deficiency, or excessive sun exposure. It occurred across varieties, across trellis systems, and across the district.

Some of these symptoms appeared last year; and as I recall appeared with the dry conditions seen in 2003 and 2004. But the widespread incidence of berry shrivel and cluster collapse was last seen in the 2000 season, when berry and cluster shrivel was rampant across the Lodi region. There are several theories about the problems seen this year, but nobody has the answer and hopefully it will be a long time before we see as many problems, in the meantime maybe we‘ll discover some clues. I think three years of drought had something to do with it (but I could be wrong as I am reminded at home). Other factors to consider are winter, spring, and summer temperatures, nutrient, crop load, and irrigation.

Vine mealybug

Vine mealybug is still spreading throughout the county. So it‘s good to be on the lookout and aware of any new infestations, often indicated by sooty mold or excessive honeydew in clusters, spurs or cordons. A high degree of ant activity in and around vines can also indicate problem spots. Good places to begin looking before harvest are where birds tend to roost. Good news lately has been the re-registration of an effective control material, along with several newer options.

With more habitat areas and native/natural landscapes, less use of residual herbicides and increased tolerance for weeds, it is more important than ever to monitor and to control some of the more noxious and troublesome weeds before they seed. Besides mare‘s tail and fleabane, yellow starthistle is also more of a problem along roadsides and it requires attention or it will dominate mowed areas, row middles, and habitats.

For many varieties such as Pinot grigio, Petite Sirah, Sauvignon blanc, Zinfandel, Colombard, even Chardonnay, and the newcomer Pinot noir; demand is good and prices may improve slightly. The demand for Cabernet Sauvignon is dramatically improved and Merlot is less of a concern, especially as the crop is below average.

The number of small wineries grows and with more labels along with more medals, everyone benefits from recognition for all the hard work and risk. The county as a whole and the Lodi District in particular continues to confirm the region to be a good place to grow quality fruit for quality wines, which are a value, in spite of the challenges to comply with new regulations while controlling costs. The economy will determine how good a year 2010 turns out to be with regard to returns, but quality is excellent and the long-term still bright.

Good luck as 2010 winds down.

Fall checklist

• If the weather stays dry, post harvest irrigation to help maintain soil moisture is more than okay until rains are steady.

• Little to no nitrogen should be applied now, but potassium now (or early next year) is okay. It won‘t move like nitrogen. To get full benefit of compost, it needs to be disked in.

• Make a note of any problem weed species that may be increasing.

• Mark any vines with excessive red leaves and/or leaf roll for monitoring of fruit quality next year or for possible removal before then.

• Renew your Ag Waiver Discharge membership.

• Update your air pollution mitigation plan if you have 100 acres or more in a single vineyard.

• Also, review your pesticide use reports and get every-thing up to date as there is continued interest to keep agriculture accountable for problems real and perceived.

• For VMB, Lorsban (chlorpyrifos) post harvest can help keep it checked until the summer control program. The new material Movento has performed well in research trials as a post harvest alternative. Be careful of sprays before a storm, especially near natural drains and waterways.

• Gophers, voles and squirrel activity are still common and may deserve attention with baits, gas cartridges, fumigant pellets (usually better in spring), trapping, shooting, or a combination of several of the methods. Remember ground squirrels are fair game, tree squirrels require a depredation permit. Owl boxes can help stabilize rodent populations, but do not control them.